1. Field of the Invention
The present invention relates to an undercut self-cutting anchor including an anchor rod having a stem provided with load application means at its rear end and with a head portion at its opposite end, with the head portion having a diameter increasing toward a front end of the anchor rod, and an expansion sleeve longitudinally displaceable over the head portion and having, at its end adjacent to the head portion, a plurality of expansion tabs separated from each other by longitudinal slots and extending in a direction toward the head portion.
2. Description of the Prior Art
In anchoring technology, it is often necessary to form connections which are expansion pressure-free to the greatest possible extent. In particular, with small edge and axis distances, the anchoring with conventional spreading anchors or dowels involves a danger of fracture of a constructional component and even of its stratification. For such distance-critical and for many reliability-critical connections, anchoring systems are used with which a specifically formed attachment member, usually formed of metal, is formed lockingly anchored in a prepared bore formed in a constructional component. To this end, the bore is provided, at a certain depth, with an undercut. The attachment member, which is to be anchored in the prepared bore, includes an anchor rod having a head portion the diameter of which increases toward the free end of the anchor rod, and an expansion sleeve having a plurality of expansion tabs separated from each other by axial slots. The relative displacement between the expansion sleeve and the anchor rod provides for radial displacement of the expansion tabs, which slides over the head portion of the anchor rod, into the undercut.
In many cases for forming an undercut a special tool, which is equipped with cutters and is eccentrically rotatable in the bore, is used. The tool removes material from the wall of the preliminary formed bore by milling or shaving to widen the wall at a desired depth. Also known are undercut self-cutting anchors which automatically form an undercut during a setting process. German Publication DE-A-31 46 027 discloses an undercut self-cutting anchor which forms an undercut by removing the wall material by chiseling as a result of axial displacement of the expansion sleeve along the anchor rod supported on the bore bottom. Another type of an undercut self-cutting anchor is disclosed in U.S. Pat. No. 4,702,654. The anchor disclosed in this U.S. patent forms an undercut by milling and shearing the bore wall material. To this end, the expansion sleeve is additionally rotated upon being axially displaced along an anchor rod which is supported on the bore bottom. The expansion tabs of the expansion sleeve are provided with cutters which remove the wall material during rotation of the sleeve and thereby form an undercut.
A drawback of the known undercut self-cutting anchor consists in that the tractrix of the expansion tabs, i.e., the curve course which is described by the outer profile of the expansion tabs in a longitudinal direction during their expansion, does not correspond to the cutting curve which defines the profile of the undercut. Therefore, often the expansion tabs only linearly engage the undercut surface in their end position. As a result, the load is lead into the constructional component non-uniformly. Only after a pre-stress of the undercut self-cutting anchor, an approximately surface engagement is provided, which is accompanied by overpressure in the contact region of the constructional component and by deformation of the expansion tabs. At that, the constructional component can be overstressed, which can adversely affect the desired holding values.
Accordingly, an object of the present invention is to eliminate the drawbacks of the prior art undercut self-cutting anchor. Another object of the present invention is to provide an undercut self-cutting anchor which would create preconditions for a most possible uniform load lead-in into the constructional component. Yet another objection of the present invention is to provide an undercut self-cutting anchor which would insure a very high load-bearing capability of the anchor. A further object of the invention is an undercut self-cutting anchor which would prevent a distortion of the constructional component in the region of the undercut upon application of a load.